Parse failure on func(arg:)) syntax

[chrishulton]

Issue Summary

The parser fails with expected expression for syntax like the following:

return uti.flatMap(mimeType(uti:))

I included a sample of code from kickstarter/ios-oss, and have a few additional examples included below.

The sample code does seem to run successfully with swift 4.

Environment

• OS Info: macOS Version 10.13.2 (Build 17C88)
• Yanagiba/swift-ast version: 0.4.1

Reproduction Steps

Sample code

import Foundation

private func mimeType(extension: String, where: CFString? = nil) -> String? {
  let uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension,
                                                  `extension` as CFString,
                                                  `where`)?.takeRetainedValue()
  return uti.flatMap(mimeType(uti:))
}

private func mimeType(uti: CFString) -> String? {
  return UTTypeCopyPreferredTagWithClass(uti, kUTTagClassMIMEType)?.takeRetainedValue() as String?
}

Command to run swift-ast with the code above:
swift-ast /Users/chrishulton/code/testing/swift_qa/failing_cases/expected_expression.swift

Expected Result

The code should be able to be parsed.

Actual Behavior

There is a fatal error: expected expression

/Users/chrishulton/code/testing/swift_qa/failing_cases/expected_expression.swift:7:35 fatal: expectedExpr

Even Better

Here are a few additional failing files for this case:

• https://github.com/kickstarter/ios-oss/blob/master/Kickstarter-iOS/DataSources/LiveStreamDiscoveryDataSource.swift#L14
• https://github.com/kickstarter/ios-oss/blob/master/Kickstarter-iOS/ViewModels/AppDelegateViewModel.swift#L273
• https://github.com/kickstarter/ios-oss/blob/master/Kickstarter-iOS/Views/Controllers/LiveVideoViewController.swift#L36

Let me know if I can provide any more information! Thanks!

[ryuichis]

If this is something obvious, please pardon me for my ignorance, but I don't see this syntax defined in swift language reference, nor I personally wrote this kind of code in the past. Could you explain me how to interpret this return uti.flatMap(mimeType(uti:))? especially what uti does in this case? Is it the argument name? Then what's the value for that parameter? Somehow it got inferred based on context or this is the value? I am confused here.

[ryuichis]

Ah, I think I know what's going on here... flatMap can take a function type as its value, and mineType(uti:) is the signature of the reference function...

Thanks for informing me this case. I will try to work on a fix soon.

[ryuichi-assistant]

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